Conventionally, for the configuration of the inkjet printhead (hereinafter “printhead”), a variety of printheads comprised of a plurality of printing elements arranged in a row, or in a plurality of rows, is well known.
With such a printhead, a configuration is known that provides a concurrently drivable control wiring terminal that places N printing elements on one block and the printing elements are powered during a period in which the terminal is activated so as to enable printing onto the printing medium.
Moreover, a configuration is known that mounts several or even tens of concurrently drivable drive integrated circuits, placing N printing elements on one block, on a single substrate and aligning image data with the printing elements so as to enable printing onto the printing medium.
Thus, as printing has become of higher resolution and higher quality, the performance of the printhead has markedly improved. Throughput has been improved by increasing the number of printing elements mounted on the printhead or by increasing the number of printing elements that are concurrently driven so as to increase print speed. In addition, the performance of the printing elements themselves has advanced, so that it is now possible to discharge amounts of ink as small as several pico-liters (pl) with a drive signal having a pulse width on the order of 1 micro-second. This advance has been made possible by using functional elements (MOS-FET drivers and the like) for switching large amounts of current at high speed. These functional elements, too, continue to be downsized year after year, and as a result, multi-channel (that is, ink channels of multiple colors) inkjet printhead substrates (hereinafter “printhead substrates”) also continue to be downsized.
For example, in order to achieve such printhead downsizing, there are also configurations that centralize signal processing circuits such as a latch circuit, a shift register and a decoder at a single location on the printhead substrate, as disclosed, for example, in Japanese Patent Application Laid-open No. 11-300973, with the printhead substrate comprised of printing elements themselves comprised of an ink supply port in the form of an elongated trench for supplying ink, electrothermal transducers along both sides of the ink supply port, and drive elements that drive the electrothermal transducers.
Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 11-245409, there are also configurations in which an ink supply port, a printing element array, a driving circuit, another printing element array and another ink supply port are arranged in order, and the driving circuit drives both of these printing element arrays.
In particular, the need for multi-channel printheads for use mainly in compact color inkjet printheads has increased recently, because devices that can form color images at low cost are indispensable to contemporary product constructions. Several methods involving ink channels of multiple colors disposed on the same substrate have been conventionally known.
For example, there is a method involving a type that arranges the printing elements into a single row and divides the ink supply ports and ink channels by color, and allocating one row of printing element arrays to each of the plurality of ink channels. Further, a method has been proposed that disposes the printing element arrays along both sides of each of the multiple ink channels. These configurations are technical approaches indispensable to achieving high-speed, high-resolution printing, and hereafter the technical problem will be how far can downsizing proceed.
Printhead types, too, extend over a wide variety of equipment types geared to the performances of the printing apparatuses that mount the printheads, and their control circuits have become more complex. Finding the optimum disposition of the control circuits on the substrate required for the configuration of high-speed, high-resolution printheads comprised of multi-ink channels including these types of circuits is the main technical problem.
In a printing apparatus using a printhead as described above, in order to increase the print speed or increase the print density, there is a tendency to increase the number as well as the density of the printing elements provided on the printhead. As a result, the number of blocks involved when time-divisionally driving these printing elements is also increasing, with a consequent increase in the number of control signal lines as well even with the use of decoder circuits and the like.
For example, in a multi-channel printhead comprised of 256 or more printing elements in one row, a minimum combination for achieving full color printing requires the provision of three colors: cyan, yellow and magenta. The control circuits for matching the printing elements with the color image data and turning each printing element ON/OFF undergo a massive increase, with the surface area of the multi-channel printhead substrate required by just the control wiring alone reaching levels that cannot be ignored. Further, arranging printing element arrays along both sides of the ink channels requires doubling the surface area of the printhead substrate under the conventional methods and obstructs the manufacture of low-cost color inkjet printing apparatuses.
Further, in printing apparatuses that use a multi-channel printhead, the printing elements disposed opposite the ink channels are of a variety of configurations.
Basically, the two rows of printing elements disposed opposite both sides of a flow path of a single ink channel can discharge ink of the same color. In the case of such a configuration, depending on the image print process of the printing apparatus, it is possible to use a configuration that further varies the ink discharge amount even for the same color by varying the diameter of the nozzles of the printing elements and the size of the electrothermal transducers of the printing elements.
For example, by disposing the printing element arrays along both sides of the ink channel so that the ink is discharged at the same position in the arrayed direction of the printing elements, printing can be completed at twice the speed of a conventional arrangement.
Additionally, by disposing one of the rows of printing elements so as to be offset from the other row of printing elements by half a pitch in the arrayed direction of the printing elements, a multi-channel printhead substrate can be configured that has twice the resolution of the conventional arrangement.
Further, varying the ink discharge amount discharged from the printing elements belonging to each of the two rows of printing elements makes possible a printing method that can achieve high-speed, high-density printing by switching among multiple modes of the printing apparatus.
The more the image quality and functions of printing apparatuses that use multi-channel printheads, as described above the more complicated the configurations of the printhead and the peripheral control devices become, and the more difficult their control becomes as well. As a result, in order to simplify the control unit on the printing apparatus main unit side, the printhead substrate has come to be loaded with as many control circuits as possible.
Moreover, when managing/executing a control sequence that would, for example, change the drive pattern of the printing elements so as to match the print mode of the printing apparatus, in a case where inconsistencies in the manufacture of the printhead or differences between manufactured lots is large, these differences in print state can be heavily reflected in the printed image, and as a result, the functions required of a multi-channel printhead, in terms of management and calibration, and further, of distinguishing between types of printheads and of continuously monitoring the drive state, only increase.
However, the control circuits and the huge number of printing elements needed in order to implement these functions push up the cost of the printhead and are a major impediment to the spread of printing apparatuses.